Summary of work: There are two major lines of research: (1) structure- function relationship of beta-amyloid peptide, i.e., how the structure of the peptide relates to its toxicity; (2) proteolytic degradation of beta-amyloid peptide in the rat, a species not susceptible to Alzheimer's pathology. (1) Electropsray mass spectrophotometric study was used to assess the state of aggregation and conformation of solutions of synthetic beta-amyloid. The toxic status of the beta-amyloid solutions (made in sterile water) was characterized with the Congo red assay. Mass spectrometry results showed that aggregation of the peptide was found in both the toxic and nontoxic forms of beta-amyloid. However, secondary conformation of the peptide was differentially reflective of toxicity, as revealed by an average charge state analysis. Toxic beta-amyloid solutions were consistent with a beta-pleated sheet conformation whereas nontoxic solutions were consistent with a random coil conformation. These results suggest that the primary event distinguishing toxic solutions of beta-amyloid is a structural transition from random coil to beta-pleated sheet. (2) Rodents do not exhibit any signs of Alzheimer's disease pathology even though they express an amyloid precursor protein that is highly homologous to the human APP. Thus, the rat brain appears resistant to the toxic effects of beta-amyloid protein. In this project, an assay was developed to confirm the catabolism of beta-amyloid by rodent brain. The effects of protease inhibitors on the fate of beta-amyloid in rat brain homogenate was also investigated. In the presence of rat brain homogenate, the beta-amyloid signal decreased in a linear fashion, as monitored by Western blots probed with an anti-beta-amyloid antibody. However, in the presence of protease inhibitors, the beta-amyloid signal appeared aggregated. The monomer band increased in intensity, a dimer-like band appeared, and high molecular weight material remained in the well of the gel. This assay will be used to identify specific proteases and/or inhibitors involved and subcellular fractions containing the proteolytic activity will be identified. This assay may be applicable to studies of normal compared with Alzheimer's diseased brains.